KR20210051406A - Method for treating waste water containing suspended solids - Google Patents

Abstract

The present invention relates to a method for treating wastewater, and more specifically, to a method for treating wastewater, which can effectively precipitate smaller and more solid suspended material in wastewater even with a small amount of heavy metals to achieve process efficiency and economical efficiency in subsequent processes by including the steps of: adding a cationic polymer having an intrinsic viscosity of 0.2 to 6.6 dl/g to wastewater containing suspended material to increase the zeta potential of wastewater to -50 to -0.01 mV; and precipitating suspended material by adding a coagulant containing heavy metals to the wastewater.

Description

Wastewater treatment method containing suspended solids {METHOD FOR TREATING WASTE WATER CONTAINING SUSPENDED SOLIDS}

The present invention relates to a method for treating wastewater containing suspended solids.

Combined Sewer Overflows (CSOs), which are non-point sources of pollution discharged through sewage pipes in rainy weather, and wastewater including household sewage and factory wastewater are the causes of water and soil pollution.

Conventional methods of purifying wastewater include activated sludge method (SBR), wood fermentation compost method, liquid corrosion method, quicklime stabilization reaction method, panton oxidation method and oxidation catalytic reaction method.

Activated sludge method (SBR), woody fermented compost method, liquid corrosion method, quicklime stabilization reaction method, etc. are too high and the wastewater treatment period is too long, so the facility cost is very high. There are drawbacks. In addition, if the pontoon oxidation method include a hydroxyl group (OH ^-) because the use of hydrogen peroxide OH due to the activation of ^- the higher the radical can dramatically decrease the concentration of the contamination, but has the disadvantage that the processing cost is extremely high, the oxidation catalyst Reaction In the case of, the wastewater purification process is a wastewater purification process based on ion exchange between wastewater and metal sulfate, which is a substrate, and the wastewater treatment cost is high, and the pollution concentration varies depending on the wastewater component. Since it is necessary, there are many problems in putting these methods into practical use.

In addition, there is a method of treating a coagulant containing an anionic polymer and a heavy metal in order to coagulate suspended substances in wastewater, but there is a problem in process efficiency and economy, such as a large amount of a coagulant containing heavy metals is required for coagulation.

Korean Patent Registration No. 0327735

An object of the present invention is to provide a wastewater treatment method capable of sedimenting suspended matter contained in wastewater with a small amount of heavy metals.

An object of the present invention is to provide a method for treating wastewater with a shortened filtration process.

The present invention comprises the steps of adding a cationic polymer having an intrinsic viscosity of 0.2 to 6.6 dl/g to wastewater containing suspended solids to reach the zeta potential of the wastewater to -50 to -0.01 mV; And adding a coagulant containing a heavy metal to the wastewater to precipitate the suspended matter.

The method of treating wastewater according to the present invention may further include passing the wastewater through an ultra filter (UF) membrane after sedimentation.

The method of treating wastewater according to the present invention may further include passing the wastewater passing through the UF membrane through a reverse osmosis (RO) membrane.

In the present invention, the suspended material may have a negative charge.

In the present invention, the cationic polymer may have an equivalent weight of 1 to 7 meq/g.

In the present invention, the cationic polymer may have a molecular weight of ^{15×10 4} to 50×10 ^{4 g/mol.}

In the present invention, the cationic polymer may be added to 1 to 10 mg/L of wastewater.

In the present invention, the coagulant containing heavy metal may be an Fe-based coagulant.

In the present invention, the zeta potential may be -30 to -0.05 mV.

In the present invention, the heavy metal may be added in an amount of 400 mg/L or less with respect to wastewater.

In the present invention, when the coagulant containing the heavy metal is added, the pH of the wastewater may be 9 to 12.

In the wastewater treatment method of the present invention, by adding a cationic polymer to reach the zeta potential of the wastewater to about 0 mV and then adding a coagulant, a small amount of a coagulant can effectively precipitate suspended solids in the wastewater.

The method of treating wastewater according to the present invention can shorten the filtration process by using a cationic polymer and heavy metal having a low intrinsic viscosity to agglomerate suspended solids small and hard.

1 is a schematic diagram showing a process of removing suspended substances in wastewater by adding a cationic polymer having a specific range of physical properties.
2 is a graph showing MFF values of Experimental Examples 1 to 4 and Comparative Example 3.

The present invention comprises the steps of adding a cationic polymer having an intrinsic viscosity of 0.2 to 6.6 dl/g to wastewater containing suspended solids to reach the zeta potential of the wastewater to -50 to -0.01 mV; And adding a coagulant containing a heavy metal to the wastewater to precipitate the suspended matter.

The method of treating wastewater according to the present invention may further include passing the wastewater through a membrane after the step of precipitating the suspended solids. The membrane may be a reverse osmosis (RO) membrane, a nanofiltration (NF) membrane, an ultrafiltration (UF) membrane, a microfiltration (MF) membrane, or the like.

The method of treating wastewater according to the present invention may further include passing the wastewater through an ultra filter (UF) membrane after the step of precipitating suspended solids.

The method of treating wastewater according to the present invention may further include passing the wastewater passing through the UF membrane through a reverse osmosis (RO) membrane.

Suspended Solid (SS) is a solid contained in wastewater. The suspended material may be particles having a particle diameter of 1 µm or more floating in the wastewater, and may be charged particles.

Sewage water means at least one of sewage or wastewater, and may include, for example, household sewage, household wastewater, agricultural and livestock wastewater, dairy wastewater, food waste, food wastewater, factory wastewater, industrial wastewater, and the like.

The present invention adds a cationic polymer to wastewater. Conventionally, anionic polymers were generally used for water treatment. However, when suspended substances in wastewater have a negative charge, there is a disadvantage that suspended substances are not easily aggregated due to the addition of anionic polymers.

In addition, the intrinsic viscosity of the anionic polymer is generally 10 dl/g or more, and the intrinsic viscosity is much higher than that of the cationic polymer. When anionic polymer with high intrinsic viscosity is used, suspended solids contained in wastewater are large and sticky, so if wastewater containing the agglomerated material passes through a filter membrane (e.g., UF membrane, RO membrane), it passes through the filter. There is a problem that a sticky residue remains and it is not easy to remove the residue from the filter.

The intrinsic viscosity of the cationic polymer of the present invention is 0.2 to 6.6 dl/g, 0.3 to 6.0 dl/g, 0.4 to 5.0 dl/g, 0.5 to 4.0 dl/g, 0.6 to 3.0 dl/g, or 0.7 to 2.0 dl/g Can be

If a cationic polymer having a low intrinsic viscosity is used, the suspended matter can be relatively small and hardly agglomerated, so that it is possible to suppress clogging of the filter due to the floating matter sticking to the filter membrane used for wastewater treatment.

The equivalent weight of the cationic polymer may be 1 to 7 meq/g.

The molecular weight of the cationic polymer may be 15×10 ⁴ to 50×10 ⁴ g/mol, 20×10 ⁴ to 40×10 ⁴ g/mol, or 25×10 ⁴ to 30×10 ⁴ g/mol. If the molecular weight of the cationic polymer is too large, the pore diameter of the UF membrane may be clogged, so it is preferable to use a cationic polymer having an appropriate molecular weight.

The cationic polymer may be a compound containing nitrogen.

Cationic polymer is 0.1 to 10 mg/L, 0.1 to 9 mg/L, 0.1 to 8 mg/L, 0.1 to 7 mg/L, 0.1 to 6 mg/L, 0.1 to 5 mg/L, 0.1 To 4 mg/L, 0.1 to 3 mg/L, 0.1 to 2 mg/L, 0.1 to 1 mg/L may be added.

By adding the cationic polymer of the present invention to wastewater, the zeta potential of the wastewater is -50 to -0.01 mV, -40 to -0.02 mV, -30 to -0.05 mV, -20 to -0.1 mV, or -10 to -0.5 mV. Can reach.

By adding the cationic polymer of the present invention to wastewater, the zeta potential of the wastewater is -50 to -0.01 mV, -40 to -0.01 mV, -30 to -0.01 mV, -20 to -0.01 mV, or -10 to -0.01 mV. Can reach.

In the wastewater treatment method of the present invention, a cationic polymer is first added to the wastewater, and then a coagulant containing a heavy metal is added.

Specifically, the wastewater treatment method of the present invention includes the step of adding a coagulant containing a heavy metal after reaching the zeta potential of the wastewater to about 0 mV by adding a cationic polymer.

If a cationic polymer is first added to reach the zeta potential of wastewater near 0 mV, and then a coagulant is added, there is an advantage that even if only a small amount of the coagulant is added, suspended matter in the wastewater can be effectively precipitated.

Specifically, the coagulant containing heavy metals is 400 mg/L or less, 350 mg/L or less, 300 mg/L or less, 250 mg/L or less, 200 mg/L or less, 150 mg/L or less, 100 mg for wastewater. /L or less, 50 mg/L or less can be added.

When a large amount of chemicals are used in wastewater treatment, it is difficult to utilize the filtration process through the UF membrane, resulting in a problem that the process becomes more complicated. The wastewater treatment method of the present invention can reduce the amount of a coagulant containing heavy metals by using a small amount of a cationic polymer, thereby increasing the efficiency of the process.

The coagulant containing a heavy metal may be an Fe-based coagulant, but is not limited thereto. The Fe-based coagulant may be FeSO ₄ 7H ₂ O, Fe ₂ (SO4) ₃ , FeCl ₃ , and the like.

When a coagulant containing a heavy metal is added, the pH of the wastewater may be 9 to 12, 9.5 to 11.5, 10 to 11, and 10 to 10.5.

Example

1 is a schematic diagram showing a method of removing suspended substances in wastewater according to an embodiment of the present invention. Specific contents of Examples 1 to 4 are as follows.

Example 1

In the first wastewater (raw water), a cationic polymer C-701 (Kurita Water Industries Ltd.) with a CE value of 6.0 meq/g, an intrinsic viscosity of 0.2 dL/g, and a molecular weight of 15×10 ^{4 g/mol (Kurita Water Industries Ltd.) 1 mg/} After L was added to reach the zeta potential of wastewater near 0 mV, FeCl ₃ 60 mg/L was injected based on the volume of raw water. When the _{pH falls below 10 due to excessive injection of FeCl 3} , the pH was maintained above 10 with NaOH or other pH adjusters. The final treatment was performed by injecting the entire amount of coagulated water in which the suspended matter was agglomerated into the UF membrane.

Example 2

Cationic polymer P-702 (Kurita Water Industries Ltd.) 1 having a CE of 6.0 meq/g, an intrinsic viscosity of 0.8 dL/g, and a molecular weight of 20×10 ^{4 g/mol in the same waste water used in Example 1} After adding mg/L to reach the zeta potential of wastewater near 0 mV, 60 mg/L _{of FeCl 3 was injected based on the volume of raw water.} When the _{pH falls below 10 due to excessive injection of FeCl 3} , the pH was maintained above 10 with NaOH or other pH adjusters. The final treatment was performed by injecting the entire amount of coagulated water in which the suspended matter was agglomerated into the UF membrane.

Example 3

Cationic polymer P-707 (Kurita Water Industries Ltd.) 1 having a CE of 4.7 meq/g, an intrinsic viscosity of 1.6 dL/g, and a molecular weight of 30×10 ^{4 g/mol in the same waste water used in Example 1} After adding mg/L to reach the zeta potential of wastewater near 0 mV, 60 mg/L _{of FeCl 3 was injected based on the volume of raw water.} When the _{pH falls below 10 due to excessive injection of FeCl 3} , the pH was maintained above 10 with NaOH or other pH adjusters. The final treatment was performed by injecting the entire amount of coagulated water in which the suspended matter was agglomerated into the UF membrane.

Example 4

Cationic polymer P-709 (Kurita Water Industries Ltd.) 1 having a CE of 1 meq/g, an intrinsic viscosity of 6.6 dL/g, and a molecular weight of 50×10 ^{4 g/mol in the same waste water used in Example 1} After adding mg/L to reach the zeta potential of wastewater near 0 mV, 60 mg/L _{of FeCl 3 was injected based on the volume of raw water.} When the _{pH falls below 10 due to excessive injection of FeCl 3} , the pH was maintained above 10 with NaOH or other pH adjusters. The final treatment was performed by injecting the entire amount of coagulated water in which the suspended matter was agglomerated into the UF membrane.

Comparative example

Comparative Example 1

The entire amount was injected into the UF membrane without injection of the cationic polymer and FeCl _{3 into the wastewater used in Example 1.}

Comparative Example 2

_{60 mg/L of FeCl 3} was injected into the same waste water as the waste water used in Example 1, and after coagulation and stirring for 15 minutes, the entire amount was injected into the UF membrane.

Comparative Example 3

_{150 mg/L of FeCl 3} was injected into the same waste water as the waste water used in Example 1, followed by coagulation and stirring for 15 minutes, and then the entire amount was injected into the UF membrane.

Comparative Example 4

_{200 mg/L of FeCl 3} was injected into the same waste water as the waste water used in Example 1, followed by coagulation and stirring for 15 minutes, and then the entire amount was injected into the UF membrane.

Comparative Example 5

_{After 250 mg/L of FeCl 3} was injected into the same waste water as the waste water used in Example 1, the entire amount was injected into the UF membrane.

Comparative Example 6

_{After 300 mg/L of FeCl 3} was injected into the same waste water as the waste water used in Example 1, the entire amount was injected into the UF membrane.

Comparative Example 7

After adding 1 mg/L of an anionic polymer (Unichemical, A-101) having an intrinsic viscosity of 170 dL/g and a molecular weight of 150×10 ^{4 g/mol to the same waste water used in Example 1, raw water} _{FeCl 3} 60 mg/L was injected based on the volume of. When the _{pH falls below 10 due to excessive injection of FeCl 3} , the pH was maintained above 10 with NaOH or other pH adjusters. The final treatment was performed by injecting the entire amount of coagulated water in which the suspended matter was agglomerated into the UF membrane.

Floating matter removal and coagulation effect of Examples and Comparative Examples

In order to confirm the effect of removing suspended matter (organic matter) from the treated wastewater through the Examples and Comparative Examples, TOC (Total Organic Carbon) of the wastewater of each of the Examples and Comparative Examples was measured. In addition, in order to confirm whether post-treatment can be performed using the UF membrane after the treatment method of the present invention, the MFF (Membrane Filter Factor) of the wastewater of each Example and Comparative Example was measured.

How to measure

(1) Zeta potential measurement

_{In the Example, the zeta potential value before the addition of FeCl 3} after the cationic polymer was added and the zeta potential value before the addition of FeCl ₃ in the Comparative Example were measured. The zeta potential value was obtained by measuring the potential difference by the zeta streaming potential method, and a Zeta Check device (ParticleMetrix) was used.

(2) TOC measurement

TOC was measured using the Nonpurgeable Organic Carbon (NPOC) method of measuring residual organic carbon after acidifying the wastewater treated on the UF film of Examples and Comparative Examples and completely removing inorganic carbon. A TOC-L instrument (SHIMADZU) was used for TOC measurement. The TOC value of the untreated wastewater (raw water) was measured to be 2.8 mg/L, and when the TOC concentration of the wastewater treated on the UF membrane of Examples and Comparative Examples decreases by more than 30% based on the raw water TOC concentration, the organic matter removal ability is reduced. I saw it as excellent.

(3) MFF measurement

MFF is a criterion for confirming whether the substance to be checked is suitable for passing through the membrane. 110 ml of the substance to be checked is first passed through a filter paper of 0.45 μm and the passing time (T1) is measured, and then the substance to be checked is 0.45 After passing through a μm filter paper a second time, the passing time (T2) was measured, and the fraction of T2 to T1 (T2/T1) was calculated. If the value was less than 1.1, it was considered suitable for UF film treatment.

Measurement result

Table 1 shows TOC and MFF of Examples and Comparative Examples. 2 is a graph showing MFF values of Examples 1 to 4 and Comparative Example 5. In Table 1 below, the zeta potential represents the zeta potential of wastewater before _{FeCl 3 is added.}

division Zeta potential
(mV) TOC(mg/L) MFF Comprehensive evaluation Measures Organic matter
Evaluating removal ability value Membrane treatment evaluation Example 1 -0.09 1.68 Great 1.04 fitness Great Example 2 -0.11 1.74 Great 1.08 fitness Great Example 3 -0.11 1.86 Great 1.09 fitness Great Example 4 -0.10 1.63 Great 1.04 fitness Great Comparative Example 1 -29 2.78 Bad Not measurable incongruity Poor removal of suspended substances Comparative Example 2 -29 2.60 Bad Not measurable incongruity Poor removal of suspended substances Comparative Example 3 -29 2.24 Bad 1.1 incongruity Removal of suspended substances and poor membrane treatment Comparative Example 4 -29 2.10 Bad 1.1 incongruity Removal of suspended substances and poor membrane treatment Comparative Example 5 -29 1.73 Great 1.06 fitness Need for overdose Comparative Example 6 -29 1.71 Great 1.07 fitness Need for overdose Comparative Example 7 -20 2.42 Bad Not measurable incongruity Removal of suspended substances and poor membrane treatment

_{As in Examples 1 to 4, when FeCl 3} was added after adding a cationic polymer to wastewater to reach the zeta potential near 0 mV, even if only a small amount of FeCl ₃ was added, the MFF standard suitable for membrane treatment was reached. The ability to remove organic matter was excellent.

_{On the other hand, wastewater to which both FeCl 3} and cationic polymer were not added as in Comparative Example 1, _{wastewater to which only a small amount of FeCl 3} was added as in Comparative Example 2, and wastewater to which anionic polymer and FeCl ₃ were added as in Comparative Example 7 formed a membrane. MFF measurement was not possible because it did not pass, and the ability to remove organic matter in wastewater was not excellent.

As in Comparative Examples 3 and 4, _{when 150 to 200 mg/L of FeCl 3} was added, it could pass through the membrane, but the measured MFF value was not an optimal value, and the ability to remove organic matter in wastewater was not excellent. In addition, in the case of Comparative Examples 5 and 6, it is uneconomical because an excessive amount of chemicals is required for removing suspended substances, and it is inefficient because an additional process for removing the chemicals from wastewater is further required.

That is, in the wastewater treatment method of the present invention, a cationic polymer is first added to the wastewater to reach the zeta potential of the wastewater near 0 mV, and then FeCl ₃ as a coagulant is added to greatly reduce the amount of coagulant added, and film treatment as a subsequent step It has the advantage that it is possible to remove suspended substances in wastewater more efficiently and economically.

Claims (11)

Adding a cationic polymer having an intrinsic viscosity of 0.2 to 6.6 dl/g to wastewater containing suspended solids to reach a zeta potential of the wastewater to -50 to -0.01 mV; And precipitating the suspended matter by adding a coagulant containing a heavy metal to the wastewater.
The method of claim 1, further comprising passing the wastewater through an ultra filter (UF) membrane after the precipitation.
The method of claim 2, further comprising passing the wastewater that has passed through the UF membrane through a reverse osmosis (RO) membrane.
The method of claim 1, wherein the suspended matter has a negative charge.
The method of claim 1, wherein the cationic polymer has an equivalent weight of 1 to 7 meq/g.
The method of claim 1, wherein the cationic polymer has a molecular weight of ^{15×10 4} to 50×10 ^{4 g/mol.}
The method of claim 1, wherein the cationic polymer is added 0.1 to 10 mg/L to the waste water.
The method of claim 1, wherein the coagulant containing a heavy metal is an Fe-based coagulant.
The method of claim 1, wherein the zeta potential is -30 to -0.05 mV.
The method of claim 1, wherein the heavy metal is added in an amount of 400 mg/L or less with respect to the waste water.
The method of claim 1, wherein the wastewater has a pH of 9 to 12 when the coagulant containing the heavy metal is added.

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